Effect of M-opsin expression level on kinetic features of the dim-flash response. (A) Time to peak of the dim-flash response (c.f., , ) plotted as a function of the estimated M-opsin coexpression ratio. (B) Flash sensitivity (% saturating response per photon μm

^{−2}). The M-opsin coexpression ratio ρ was estimated as the relative sensitivity to 501- and 361-nm flashes, i.e., for each cone ρ =

*S*_{501}/

*S*_{361} (compare ) was measured. Each point plotted without error bars represents data of a single cone: for S-cones (red filled circles) ρ < 1; for M-cones (green filled circles) ρ > 1; error bars are 95% confidence intervals for pooled data (data for several S-cones with ρ ≤ 0.001 were pooled and plotted at ρ ≈ 0.001; the points in the M-cone sector with bidirectional error bars provide the mean and 95% confidence intervals for the entire M-cone populations). The gray bars plot 95% confidence region for the time to peak (

*t*_{peak}) and dim-flash sensitivity of

*G*_{t}α

^{−/−} cones; since there were no trends in these cones, their results were pooled (see ). The smooth (gray) curve in A plots an empirical relation,

*t*_{peak} (ρ) =

*t*_{peak,dark} − Δ

*t*_{peak}[ρ

^{n}/

], with

*t*_{peak,dark} = 96 ms, Δ

*t*_{peak} = 36 ms,

*n* = 2, ρ

_{0} = 0.048; 96 ms is the overall mean

*t*_{peak} for

*G*_{t}α

^{−/−} cones, while Δ

*t*_{peak} was selected so the curve would run through

*t*_{peak} for the M-cones. The gray curve in B plots the upper envelope of Eqs. 7a and 7b; the extension of the individual curves for

*S*_{361} and

*S*_{501} are shown as dashed lines. Eq. 7 has two parameters

*S*_{F,dark} and

*I*_{dark}*; we set

*S*_{F,dark} = 0.034, close to the average value for

*G*_{t}α

^{−/−} cones (), and

*I*_{dark}* = 1200 s

^{−1}.

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